Ah, good.
@Shandra, because I wasn't aware of that at the time, though using the one in opera:config would be very ill-advised, as it changes it for all sites.
The one in override.ini, mentioned in the next post, is the way to go. I wasn't aware of that either back at the time, though I would have noticed it earlier if the "User Prefs|Custom User-Agent" line ever actually appeared in the file.